The invention relates to an adhesive film strip and to its use; the invention relates in particular to a strippable, high-peel-strength, adhesive film strip having a first adhesive film strip region of high cross-sectional area, preferably realized by means of a large adhesive strip width, and adjacent to this first adhesive film strip region a second adhesive film strip region with strong spontaneous tapering of the adhesive film cross-sectional area, in association with one or more adhesive film strip ends which run to a point, the said strip featuring only very low transfer to a bonded article of the energy stored elastically in the adhesive film strip in the course of the detachment process, and so, at the end of the detachment process, in the case of double-sidedly adhesive film strips, causing no significant catapulting of the assembly comprising one of the bonded articles and the adhesive film strip, even when one of the two articles bonded to one another is not fixed during the detachment process. At the same time, the adhesive film strip in the invention features a significantly reduced drop in the energy stored elastically in it at the end of the detachment process.
The invention relates to a high-peel-strength, double-sided adhesive film strip for a bond redetachable without residue or destruction, the said strip being removable from a joint by stretching extending essentially in the bond plane such that the debonding of the two adherends proceeds very substantially simultaneously and, at the end of the detachment process, there is no significant catapulting of the assembly comprising one of the bonded articles with the adhesive strip. At the same time, the adhesive film strip of the invention features only a very slight drop in the elastic energy stored in it during the detachment process.
The invention further relates to a high-peel-strength, single-sided adhesive film strip for a bond redetachable without residue or destruction, the said strip being detachable by stretching extending essentially in the bond plane such that at the end of the detachment process there is only a very slight drop in the energy stored elastically in the said strip, as a result of which there is only a very low transfer to the bonded article of the energy stored elastically in the adhesive strip during the detachment process.
Highly elastically or plastically extensible (strippable) self-adhesive tapes which are redetachable without residue or destruction by stretching extending essentially in the bond plane are known from U.S. Pat. No. 4,024,312, DE 33 31 016, WO 92/11332, WO 92/11333, DE 42 22 849, WO 95/06691, DE 195 31 696, DE 196 26 870, DE 196 49 727, DE 196 49 728, DE 196 49 729 and DE 197 08 366.
They are frequently used in the form of single- or double-sided adhesive film strips (adhesive tape strips, adhesive strips), which preferably have a nonadhesive grip-tab region from which the detachment process is initiated. Particular applications of such self-adhesive tapes may be found, inter alia, in DE 42 33 872, DE 195 11 288, U.S. Pat. Nos. 5,507,464, 5,672,402 and WO 94/21157. Specific embodiments are described, for example, in DE 44 28 587, DE 44 31 914, WO 97/07172, DE 196 27 400, WO 98/03601 and DE 196 49 636.
A highly advantageous quality criterion of abovementioned strippable adhesive film strips is their capacity to develop a reduced adhesion under stretching, including that involved in the detachment process, as a result of which the friction of the adhesive strips on the edges of the adherends, and thus the mechanical load on the adhesive strips in these potential contact regions, when corresponding double-sided adhesive film strips are removed from the joint, are low. An essential factor, especially for the redetachable bonding of rigid adherends, is a reduction in the thickness of the adhesive film strip during detachment, which is the primary prerequisite for the ability to remove double-sided adhesive tapes from a joint.
The realization of strippable self-adhesive tapes which on the one hand have high peel strength by virtue of a large adhesive-strip width and on the other hand may be reliably redetached without residue, destruction or tearing in all cases, even from very sensitive substrates, is a complex undertaking and requires further preconditions. With regard to redetachment without residue, destruction or tearing, DE 44 31 914 and DE 196 49 636 address in particular the problem of tears in the grip-tab region and, respectively, in the adhesive-strip region directly adjacent to the grip-tab region. DE 44 28 587 describes an adhesive film strip for a rereleasable bond removable from a joint by pulling in the direction of the bond plane, characterized in that the bond area decreases towards the end of the adhesive film strip (the end which disappears in the joint) (see claim 1). DE 44 28 587 describes pointed, zigzag, convexly curved, and corrugated adhesive film strip ends. Essential in each case is a reduction in the bond area at the end of the adhesive strip (column 1, lines 63 and 64). Correspondingly shaped adhesive film strips, in comparison to adhesive film strips whose bond area does not decrease at the end, exhibit a significantly reduced tendency to tear in the end region of the adhesive strips. At the same time, there is a marked reduction in instances of substrate damage, so that even very sensitive substrates may be reversibly bonded with such adhesive film strips.
A further problem may be the transfer to an adherend of the energy stored elastically during the stripping process in the adhesive strip which it is intended to detach. In the case of double-sided adhesive film strips, there may be catapulting of the assembly comprising adhesive strip for detachment and one of the bonded articles, and this catapulting may cause not inconsiderable damage. Furthermore, the spontaneous elastic release of, in particular, highly elastic strippable self-adhesive tapes at the end of the stripping process (viz, at the end of the detachment process, the drop in the energy stored elastically in the adhesive strip during the detachment process) may result in the adhesive tape snapping back against the fingers, which may have very painful consequences.
WO 97/07172 addresses the specific problems of the catapulting of articles bonded with strippable double-sided self-adhesive tapes and of the spontaneous snap-back of aforementioned self-adhesive tapes from the joint at the end of the detachment process. Catapulting of bonded articles may occur when, at the end of the detachment process, the adhesive strip for detachment has separated only from one of the adherends, e.g. the wall, and the second adherend is not adequately fixed. The energy elastically stored in the self-adhesive strip in the course of its stretching then causes the assembly comprising adhesive strip and the unfixed article, still bonded to the adhesive film strip, to catapult in the direction of detachment. The solution described by WO 97/07172 is a strippable self-adhesive strip which on one adhesive surface at the end of the adhesive strip has a region of no adhesion or else significantly reduced adhesion (differential adhesive strip end). If this self-adhesive strip surface is directed towards the bonded article, then when the adhesive strip is detached there is first of all complete separation of the adhesive strip from the bonded article, so that the latter is detached from the bond substrate and can be removed therefrom, and on further stretching of the self-adhesive tape the same then detaches from the second substrate, e.g. the wall. Aforementioned adhesive strips therefore permit controllable sequential detachment of an adhesive bond. The thus-controlled sequential detachment process likewise reduces the snap-back of the adhesive film strip from the joint by virtue of the absence of one adherend (which has in fact already undergone detachment).
Without a non-adhesive or significantly adhesion-reduced end region, the detachment sequence of two bonded articles is normally not easy to control. Rather it is observed, for example in the case of a poster affixed to a wall with a strippable self-adhesive tape not designed in accordance with WO 97/07172, unless fixed during the detachment process, that at the end of the detachment process the poster is accelerated together with the adhesive strip in catapult fashion in the detachment direction. In this case, therefore, there is first of all complete detachment of the self-adhesive tape from the wall; in the instant of complete detachment of the adhesive strip from the wall, the strip has not yet separated fully from the poster. Subsequently, the energy stored elastically in the strip during its stretching process results in the catapulting of the bonded article, in this case the poster, in the detachment direction. Sensitive materials in particular, such as posters, for example, which use very thin papers of low tear strength, may thus easily be damaged during the detachment process. Owing to the catapult-type acceleration at the end of the detachment process and subsequent collision with another article, solid materials may be damaged or cause damage to the said article. In particular, the impact on the fingers of bonded articles accelerated in catapult fashion may be very painful and may also cause injury. Although sensitive flexible materials, such as posters, for example, are pressed firmly onto the bond substrate, the region between the adhesive strip for detachment and the point at which the poster is pressed onto the bond substrate is not tautly fixed (in other words, if the poster paper forms, for example, a wavelike bulge between the region in which it is fixed on the substrate with the adhesive film strip and the point at which it is pressed onto the substrate using, for example, the hand), with low-strength poster papers a very frequent occurrence is tearing at the end of the detachment process, since at the end of the detachment process the poster with the adhesive strip may initially be accelerated in the detachment direction but then, after a short acceleration path, is suddenly stopped, and so undergoes very high negative acceleration, which may lead to the tearing of the poster paper. Although the catapulting of articles fastened with strippable self-adhesive strips may be reliably avoided by taut fixing thereof during the detachment process, it is found in practice that inexperienced users in particular, and children as well, do not always perform such fixing, frequently with corresponding damage to the bonded articles or to the user themselves.
Although for numerous product structures comprising double-sided strippable self-adhesive tapes, the measures described in WO 97/07172 afford effective protection against the specific problem of the catapulting of bonded articles, there are numerous problems that remain unsolved or new problems which arise as a result of the specific product structure required:
1. A not inconsiderable effort is required to equip adhesive strips such that they possess a differential adhesive strip end.
2. The main problem, however, is that the user of such self-adhesive strips is required to apply them with the correct assignment of the adhesive faces to the adherends. Consequently, the correct usage of the self-adhesive strips requires not only that the orientation of the grip tab be performed correctly but also that the correct self-adhesive strip surface, i.e. that with the non-adhesive or adhesion-reduced end region, is directed towards the bonded article. Especially when bonding two or more similar articles to one another, the advantage of sequential detachment can seldom be exploited in practice, since the user can hardly be expected to recall which side of the self-adhesive strip is on which adherend.
3. If the article for removal is not fixed during detachment of the strippable self-adhesive strip, further problems arise. In the case of incorrect orientation of the adhesive strip provided with a differential adhesive strip end, the catapulting of an article fixed, for example, on a wall is manifested to an even greater extent: in the instant of detachment of the adhesive strip from the wall, the entire stripping force is transferred in each case to the fixed object, which may lead to a very severe catapult effect.
As remarked above, DE 44 28 587 describes adhesive film strips for a redetachable bond removable from a joint by pulling in the direction of the bond plane. The essential factor in each case is a reduction in the bond area at the end of the adhesive strip (column 1, lines 63 and 64). DE 44 28 587 describes pointed, zigzag, convexly curved, and corrugated adhesive film strip ends. The problems of the catapulting of bonded articles and of the spontaneous snap-back of strippable adhesive strips at the end of the detachment process are not addressed in DE 44 28 587. Nor are they reliably excluded by the measures proposed. Similarly, DE 44 28 587 gives no indications as to how, at the end of the detachment process, a very small drop in the elastic energy stored in the adhesive strips in the course of extensive detachment may be realized.
The aim of the present invention was to specify a double-sided self-adhesive strip which
has a high peel strength,
by virtue of substantially simultaneous detachment of both adherends features no significant catapulting of bonded articles at the end of the detachment process, even when one of the bonded articles is not fixed during the detachment process,
by virtue of its product structure requires no particular allocation of the adhesive strip sides to the adherends, and thus
does not necessitate separate asymmetric treatment by means of a non-adhesive end region, and
at the end of the detachment process features only a very small drop in the energy stored elastically in the adhesive strip in the course of its extensive detachment.
A further aim of the present invention was to provide a single-sided self-adhesive strip which by virtue of its special shape
has a high peel strength,
at the end of the detachment process, features only very low transfer to the bonded article of the energy stored in the adhesive strip during detachment, and
at the end of the detachment process, causes only a very low drop in the energy stored elastically in the adhesive strip in the course of its extensive detachment.
The above is achieved surprisingly by means of a self-adhesive strip which in practical use under virtually all application conditions features a high rate of detachment at the end of the detachment process. Rapid detachment by the user is of course promoted by the realization of low stripping forces, which is possible, for example, by means of low adhesive-strip thicknesses or low adhesive-strip widths and/or widths of the adhesive regions, measures which, however, in respect of the tensile strength required for reliable detachment (in the case of very thin adhesive strips) or in a limited bond area (in the case of very narrow adhesive strips or very narrow adhesive regions) are manifested in a disadvantageous manner. It has now been found that very high peel strengths are achieved and, likewise, that very high detachment rates in the end region of the adhesive strips are realized by means of adhesive strip shapes comprising a first pressure-sensitive adhesive region, adjacent for example to the optional adhesive-strip grip tab present, the said pressure-sensitive adhesive region being of comparatively high cross-sectional area (realized, for example, by means of a large width and thickness of the adhesive strip), adjacent to which there is a second adhesive strip region of highly decreasing or tapering cross-sectional area (realized, for example, by means of a pressure-sensitive adhesive region which tapers greatly in width), which opens at the end of the adhesive strip into one or more adhesive-strip ends which run to a point. Essential to high peel strengths is the adhesive-strip width in the abovementioned first adhesive-strip region of high cross-sectional area; essential to high detachment rates at the end of the detachment process is a comparatively high detachment force (stripping force) in the first abovementioned pressure-sensitive adhesive-strip region (the user has to pull forcefully in order to remove the adhesive strip from the joint), which force then drops significantly within a short distance in the second abovementioned adhesive-strip region, so that the detachment process is continued at a sharply accelerated rate. Essential to a small drop in the energy stored elastically in the adhesive strip during the detachment process is the adhesive-strip end which converges in one or more points.
Preferred adhesive-strip shapes feature a first region of high cross-sectional area of the adhesive strip regions, which is preferably realized by way of a high adhesive-strip width. Preferred adhesive-strip widths in this first adhesive-strip region are between approximately 8 mm and approximately 30 mm, with particular preference between approximately 10 mm and approximately 25 mm. Preferred stripping forces in the first adhesive-strip region are on average greater than approximately 5 N, with particular preference greater than 10 N (stripping force measured for white typewriter paper {basis weight: 80 g/m2} bonded to coated woodchip wallpaper; see under Test Methods). Adjacent to the first adhesive-strip region of high cross-sectional area, preferably realized by means of a high adhesive-strip width, there is a second adhesive-strip region in which the cross-sectional area of the adhesive strip regions reduces significantly within a short distance. Preferably, a reduction is achieved in the adhesive-strip cross-sectional area by more than approximately 60%, with particular preference more than 75%, within an adhesive-strip length of less than approximately 50% of the adhesive-strip width at the end of the first adhesive-strip region, preferably of less than 35% of the adhesive-strip width at the end of the first adhesive-strip region. Adhesive-strip ends are shaped so as to run out to a point. One or more adhesive-strip ends which run out to a point are possible. Within the adhesive-strip points, angles between adhesive-strip edges which converge to a point are less than 35xc2x0, preferably less than 20xc2x0, with particular preference less than 15xc2x0. Curvature radii of the adhesive-strip ends are less than 0.5 mm, preferably less than 0.3 mm. The overall length of the adhesive strips is greater than approximately 20 mm, preferred lengths are from approximately 25 mm to 100 mm, although in principle greater lengths may also be used in accordance with the inventionxe2x80x94with particular preference, they are from 30 mm to 65 mm.
The detachment rate of strippable self-adhesive tapes may be described by the separation rate of the moving grip tab, VA, or by the rate of the adhesive composition detaching from the substrate, VPSA. In the steady-state case (constant peel rate, constant adhesive-strip width and adhesive-strip thickness), both variables are proportional to one another. The proportionality constant is defined in this case by the instantaneous extension of the adhesive strip. The observed reduction in the sudden drop of the energy stored elastically in the adhesive strip (which causes catapulting) probably also occurs as a result of the fact that adhesive strips which taper in their cross-sectional area and/or in their width, owing to the equally steadily reducing detachment force in the region of the adhesive-strip tapering, exhibit a significantly lower ratio of VA/VPSA; i.e., at the same separation rate of the grip tab, a higher rate of the adhesive composition detaching from the substrate is established.
Apart from by integrating an adhesive-strip region which reduces in width, high detachment rates at the end of the detachment process may also be realized by means of a corresponding reduction in the adhesive-strip thickness or by means of a reduction in the bond strength in the course of the detachment process (for example, by rendering the pressure-sensitive adhesive composition inert progressively on both sides in accordance with DE 44 28 587) or by means of a combination of the aforementioned possibilities.
As a further advantage, self-adhesive tapes of the invention possess, in the end region of the adhesive strips, an outstanding capacity for tear-free and residue-free redetachment, including for redetachment from highly sensitive substrates, such as sensitive wallpapers, for example, or from substrates having a very high sticking tendency, such as metal, glass or polar plastics surfaces, for example.